Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.80   13.860%   $228.6309   $228.63   $228.65   $228.60  
  Purchase #2 $238.93   11.431%   $266.2421   $266.24   $266.25   $266.20  
  Purchase #3 $96.87   10.158%   $106.7101   $106.71   $106.70   $106.70  
  Purchase #4 $30.51   6.461%   $32.4813   $32.48   $32.50   $32.50  
  Purchase #5 $39.77   12.667%   $44.8077   $44.81   $44.80   $44.80  
  Purchase #6 $177.55   10.456%   $196.1146   $196.11   $196.10   $196.10  
  Purchase #7 $121.55   11.352%   $135.3484   $135.35   $135.35   $135.30  
  7 purchase totals = $905.98       $1,010.3351   $1,010.33   $1,010.35   $1,010.20